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video related to potentiometer
video related to potentiometer
A potentiometer (also known as a pot or potmeter) is a three-terminal variable resistor whose resistance can be manually adjusted to control the flow of electric current. A potentiometer is a variable voltage divider.
As a potentiometer measures using null or balance conditions, hence no power is required for the measurement.
Null method: a measurement method in which an unknown quantity (such as electric current) is compared (as in a Wheatstone bridge) with a known quantity of the same kind and found to be equal by the detector's zero response.
The actual quantity measured is the terminal voltage V, which is related to the emf of the battery by V=emfIr, where I is the current flowing and r is the battery's internal resistance.
The emf could be calculated precisely if r were known precisely, but this is not usually the case. If the current I could be reduced to zero, V=emf, and thus emf could be measured directly
Basic principles of potentiometer:
Connect 2 batteries in parallel through a galvanometer.
The negative battery terminals are connected together and positive battery terminals are also connected together through a galvanometer.
If the emf battery for both batteries are different it will cause the galvanometer to deflect.
If the emf for both batteries are the same so there is no deflection.
TYPE OF POTENTIOMETER
1)SLIDE WIRE
2) VOLTBOX
3)SINGLE RANGE DIAL
SLIDE WIRE
Principle: the potential dropped across a segment of a wire of uniform cross-section carrying a constant current is directly proportional to its length.
Calibration method: determine the relationship between the analytical response from the instrument and the analyte concentration.
Initial measurement, the potentiometer must be calibrated.
The switch is closed, the working current will flow through the slide wire and the rheostat.
The value of this current can be modified by adjusting the rheostat.
Unknown measuring process: measure voltage by comparison of an unknown voltage with known voltage.
VOLTBOX
Definition: Used to expend the voltage measurement range of a basic potentiometer circuit.
It uses the voltage divider concept to reduce the large unknown voltage Vinput.
A proper range of resistance must be chosen so that the output voltage from the voltbox is not more than the measurement range of the potentiometer.
The resistance value (in series) must be added respectively for every range.
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